The Colosseum is definitely one of Rome's main tourist attractions and is considered one of the 7 wonders of the world. It could hold 40,000 seated spectators (and another 10,000 standing), making it the largest theater in the entire Roman Empire. It was built between 72 and 80AD by the Flavian emperors, to whom it owes its original name: the Flavian Amphitheater. The name Colosseum comes from the gigantic Colossus of Nero statue nearby which, sadly, is not standing today. The Emperor Titus inaugurated the Colosseum during a celebration lasting 100 days.
The spectacles were meant to be a form of public entertainment. Admission was free and the cost of running the events was bore by the Empire. Seating was according to social class, with the aristocratic class seated near the front and lower classes in the higher seats. There were public executions, animal hunts, dramatic plays, and all kinds of gladiator battles.